Opposing row linear concentrator architecture

ABSTRACT

A solar concentrator assembly is disclosed. The solar concentrator assembly comprises a first reflective device having a first reflective front side and a first rear side, a second reflective device having a second reflective front side and a second rear side, the second reflective device positioned such that the first reflective front side faces the second rear side, and a support assembly coupled to and supporting the first and second reflective devices, the second reflective device positioned to be vertically offset from the first reflective device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/849,606, filed Aug. 3, 2010, and titled “OPPOSING ROW LINEARCONCENTRATOR ARCHITECTURE,” the entire contents of which areincorporated by reference herein in its entirety and for all purposes.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally tosolar concentrators. More particularly, embodiments of the subjectmatter relate to concentrator component arrangements.

BACKGROUND

One challenge encountered during assembly and operation of a solarconcentrator is weight distribution. Solar concentrator arrays arefrequently mounted to, and have their position adjusted at, a centralpost or pier. Such concentrator arrays typically have a supportstructure with a lateral member, such as a crossbeam or strut. Thelateral member is typically coupled directly to the post, usually by apositioning mechanism. In turn, several concentrator elements arecoupled to the lateral member, and are supported by it.

As a consequence of the components' position above the lateral member,the center of gravity of the concentrator array is above the post, and,consequently, above the positioning mechanism. When the concentratorarray rotates to certain positions, the concentrator array canexperience an undesirable moment at the positioning mechanism caused bythe position of the center of gravity relative to the positioningmechanism. Traditionally, this is offset by a counterweight, whichincreases the overall weight of the system and increases cost, amongother undesirable effects.

Additionally, the arrangement of concentrator elements is usuallyoptimized to reduce or eliminate losses to inefficient ground cover, andthe associated overall system cost increase. The ratio of concentratoraperture to area of ground covered therefore is preferably increased ashigh as possible. One way this can be done is with numerous concentratorelements covering the available ground. Dense concentrator elements canpresent numerous challenges to efficient power conversion.

BRIEF SUMMARY

A solar concentrator assembly is disclosed. The solar concentratorassembly comprises a first reflective device having a first reflectivefront side and a first rear side, a second reflective device having asecond reflective front side and a second rear side, the secondreflective device positioned such that the first reflective front sidefaces the second rear side, and a support assembly coupled to andsupporting the first and second reflective devices, the secondreflective device positioned to be vertically offset from the firstreflective device.

Another embodiment of a solar concentrator assembly is disclosed. Thesolar concentrator assembly comprises a torque tube having a long axis,a crossbeam extending in a direction transverse to the long axis, afirst reflective device having a first reflective surface facing outwardfrom the torque tube and a first rear side facing toward the torquetube, the first reflective device supported by the crossbeam at a firstheight, and a second reflective device having a second reflectivesurface facing outward from the torque tube, the second reflectivedevice positioned in front of the first reflective surface and supportedby the crossbeam at a second height, the second height greater than thefirst height.

An embodiment of a solar array is also disclosed. The solar arraycomprises a crossbeam extending along a first axis, a torque tubeintersecting the crossbeam near the center of the crossbeam, the torquetube extending along a second axis, the second axis substantiallytransverse to the first axis, a first solar concentrating device coupledto the crossbeam at a first height, and a second solar concentratingdevice coupled to the crossbeam at a second height, the second solarconcentrating device further along the crossbeam from the torque tubethan the first solar concentrating device, and the second height higherthan the first height.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a side view of an embodiment of a solar concentrator system;

FIG. 2 is a perspective view of the solar concentrator system of FIG. 1;

FIG. 3 is a side view of an embodiment of a solar concentrator system ina rotated position;

FIG. 4 is a side view of an embodiment of a solar concentrator system ina rotated position under wind loading;

FIG. 5 is a detailed side view of an embodiment of a solar concentratorarray;

FIG. 6 is a side view of a portion of an embodiment of a solarconcentrator array; and

FIG. 7 is a side view of a portion of another embodiment of a solarconcentrator array.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

“Coupled”—The following description refers to elements or nodes orfeatures being “coupled” together. As used herein, unless expresslystated otherwise, “coupled” means that one element/node/feature isdirectly or indirectly joined to (or directly or indirectly communicateswith) another element/node/feature, and not necessarily mechanically.Thus, although the schematic shown in FIG. 5 depicts one exemplaryarrangement of elements, additional intervening elements, devices,features, or components may be present in an embodiment of the depictedsubject matter.

“Adjust”—Some elements, components, and/or features are described asbeing adjustable or adjusted. As used herein, unless expressly statedotherwise, “adjust” means to position, modify, alter, or dispose anelement or component or portion thereof as suitable to the circumstanceand embodiment. In certain cases, the element or component, or portionthereof, can remain in an unchanged position, state, and/or condition asa result of adjustment, if appropriate or desirable for the embodimentunder the circumstances. In some cases, the element or component can bealtered, changed, or modified to a new position, state, and/or conditionas a result of adjustment, if appropriate or desired.

“Inhibit”—As used herein, inhibit is used to describe a reducing orminimizing effect. When a component or feature is described asinhibiting an action, motion, or condition it may completely prevent theresult or outcome or future state completely. Additionally, “inhibit”can also refer to a reduction or lessening of the outcome, performance,and/or effect which might otherwise occur. Accordingly, when acomponent, element, or feature is referred to as inhibiting a result orstate, it need not completely prevent or eliminate the result or state.

In addition, certain terminology may also be used in the followingdescription for the purpose of reference only, and thus are not intendedto be limiting. For example, terms such as “upper”, “lower”, “above”,and “below” refer to directions in the drawings to which reference ismade. Terms such as “front”, “back”, “rear”, and “side” describe theorientation and/or location of portions of the component within aconsistent but arbitrary frame of reference which is made clear byreference to the text and the associated drawings describing thecomponent under discussion. Such terminology may include the wordsspecifically mentioned above, derivatives thereof, and words of similarimport. Similarly, the terms “first”, “second”, and other such numericalterms referring to structures do not imply a sequence or order unlessclearly indicated by the context.

Solar concentrator elements can be arranged to provide nearly completeground cover. Typical concentrator arrays have a center of gravityoffset from a rotational axis of the array. As a result of this offset,when the concentrator array is rotated such that the center of gravityis not directly above the rotational axis, such as during sun tracking,a moment is created about the rotational axis. This moment can increasethe difficulty of properly aligning the concentrator array, therebyreducing efficiency. To counter this moment, some concentrator arrayshave a counterweight, which adds to system cost and weight, neither ofwhich are desirable.

Moreover, concentrator arrays typically have successive rows ofconcentrating elements. Some such arrays have solar receiver elementsmounted to concentrator elements to conserve space and preserve groundcover. A level array of such concentrator/receiver pairs introducesundesirable paths for concentrated light to travel. For example, thelight travel distance from a concentrator reflective surface to areceiver element may be different for light reflected from oppositesides of the reflective surface. This difference can introduceundesirable characteristics, such as intensity variation during slightmisalignment. Additionally, an edge can reflect light to the solarreceiver at an undesirably steep angle, which can reduce the opticaltransmission efficiency of the system. Steep angles of incidenceoccurring at the reflective surface also reduce optical transmissionefficiency.

To inhibit these undesirable effects, solar concentrators can bearranged to have the center of gravity of the concentrator arraypositioned along the axis of rotation of the array. This reduces oreliminates the moment that would be caused by an offset center ofgravity. To prevent loss of ground cover that would be caused bypositioning a rotational member, such as a torque tube amongconcentrator elements, the concentrator elements can be arranged suchthat half face in one direction, the other half in the oppositedirection, with the torque tube positioned between.

Additionally, the concentrator elements can be offset in a verticaldirection from each other, rising higher out of a level horizontalplane, the farther they are positioned from the torque tube. This offsetcan reduce the difference in light travel distance between oppositeedges of the concentrator's reflective surface. Moreover, the angle oflight impinging on the solar receiver, relative to the surface of thesolar receiver, is adjusted to reduce the angle, and thereby lessenscattering and transmission losses. The vertical offset of theconcentrator elements also allows for a reflector design with a smallerangle of light incidence upon the surface, thus reducing opticaltransmission losses from this element.

FIGS. 1 and 2 illustrate an embodiment of a solar concentrator array orassembly 100. The drawings contained herein are for descriptive purposesand may not be to scale. Certain features may be exaggerated forexplanation. The solar concentrator assembly 100 comprises a pier orpost 102 which supports a crossbeam 104 and torque tube 106. Thecrossbeam 104 in turn supports first and second groups of concentratorelements 120, 140. The first group of concentrator elements 120 face inone direction, while the second group of concentrator elements 140 arepositioned facing the opposite direction, with the changeover betweenthem occurring at the torque tube 106. Certain elements are shown, whileothers are omitted for clarity and descriptive purposes, as will beexplained in greater detail below.

The post 102 can be a single post or one of several supporting the solarconcentrator assembly. The post 102 is preferably anchored within afoundation in the ground to support it. The post 102 can be a solid orhollow member of sufficient size and cross-sectional characteristics tosupport the solar concentrator assembly 100. The post 102 can be formedof a metal, such as steel, aluminum, and similar high-strength metals,or alternative material. For example, concrete or ceramic can be used insome embodiments, as desired.

When groups of concentrator elements are positioned laterally adjacenteach other to extend the solar concentrator assembly 100, multiple posts102 can be used, spaced appropriately, to support the entirearrangement. Thus, although only one group of concentrator elements isshown facing each direction in FIGS. 1 and 2, more groups can bepositioned along the torque tube 106, extending the solar concentratorassembly 100. Posts 102 can be positioned between every concentratorelement group or spaced further apart, as desired.

The crossbeam 104 is supported by the post 102 and torque tube 106. Asexplained in greater detail below, the crossbeam 104 can have asubstantially horizontal shape, which can include an upwardly-angledportion for positioning individual concentrator elements. The crossbeam104 can be one of several crossbeams or cross-pieces which support agiven concentrator element group. Thus, although one crossbeam 104 isshown, several lateral members can support a single concentrator elementsuccessively along the torque tube 106. The crossbeam is preferably madefrom a high-strength metal such as steel, although other materials canbe used, as desired.

The rotational member, or torque tube 106, can be mounted to, andsupported by, the post 102. The torque tube 106 is preferably mounted byor to a bearing or bushing or other assembly permitting rotation of thetorque tube 106 along its long axis. In some embodiments, a motor orother driving device can be situated between the post 102 and torquetube 106 to adjust the position of the torque tube 104, andcorrespondingly, the position of the concentrator element groups 120,140. The torque tube 106 is preferably a hollow tube with a circularcross-section, although other shapes and geometries can be used ifpreferred, including elliptical or solid shafts. The torque tube 106 hasa long axis extending along its length. The long axis extends throughthe center of the cross-section of the torque tube 106 and the torquetube rotates around it.

The torque tube 106 can extend through multiple concentrator elementgroups, including extending substantially entirely along the width ofthe concentrator elements, either as a unitary piece or by couplingtogether similar tubes. Thus, although the torque tube 106 is shown withtwo concentrator element groups 120, 140, there can be other elementgroups adjacent these, up to an appropriate limit. The torque tube 106preferably can support the weight of the crossbeam 104 and concentratorelement groups 120, 140 with minimal elastic or inelastic deforming,thereby inhibiting alignment error into the solar concentrator assembly100. The torque tube 106 is preferably rigidly mounted to thecrosspieces, including crossbeam 104, such that rotating the torque tube106 around its long axis similarly rotates the crosspieces.

The solar concentrator element groups 120, 140, directly or indirectly,are coupled to and supported by the crossbeam 104 and torque tube 106.The first concentrator element group 120 is composed of the first,second, and third concentrator elements 122, 124, 126. The secondconcentrator group 140 is composed of fourth, fifth, and sixthconcentrator elements 142, 144, 146. Each concentrator element 122, 124,126, 142, 144, 146 has a front, reflective side and a rear side. Thereflective side can be, or can include, a mirror shaped according to thegeometric characteristics of the concentrator/receiver combination toprovide concentrated sunlight on the solar receiver. The concentratorelements 122, 124, 126, 142, 144, 146 receive unconcentrated sunlightand reflect it to a solar receiver, while concentrating it to a smallerarea than the reflective surface. Preferably, the concentrator elements122, 124, 126, 142, 144, 146 have a parabolic shape, as shown, althoughother shapes can be used.

For descriptive purposes, certain aspects of the solar concentratorassembly 100 are illustrated not entirely to scale, in a differentposition, or in a different orientation than they may appear in certainembodiments. For example, concentrator elements 122, 142 are illustratedwith a greater vertical position than might be the case in someembodiments. Thus, in certain embodiments, the concentrator elements122, 142 may extend substantially entirely over the torque tube 106,thereby reducing the amount of sunlight which falls between them andincreasing the amount captured by the concentrator elements 122.Similarly, all concentrator elements 122, 124, 126, 142, 144, 146 canhave such different orientations.

The first concentrator element 122 reflects concentrated sunlight to thefirst solar receiver 132. The second concentrator element 124 reflectsconcentrated sunlight to the second solar receiver 134. The thirdconcentrator element 126 can also direct concentrated sunlight to areceiver mounted on the crossbeam 104, although it has been omitted forclarity. Similarly, the fourth and fifth concentrator elements 142, 144can direct concentrated sunlight to the third and fourth solar receivers152, 154, with the solar receiver corresponding to the sixthconcentrator element 146 omitted for clarity. The omitted solarreceivers corresponding to the third and sixth concentrator elements126, 146 can be positioned at heights and in orientations necessary tocooperate with certain techniques described herein. Thus, the offset forthe omitted receivers can correspond to the offset between the first andsecond solar receivers 132, 134 in a concentrator row.

Each solar receiver 132, 134, 152, 154 can be mounted to the rear sideof a concentrator element, as shown. The solar receivers 132, 134, 152,154 can comprise a photovoltaic solar cell, diode, interconnect, thermaladhesive, heat spreading device, encapsulant, frame, junction box and/ormicro-inverter, and other components as appropriate or desired forefficiently converting received concentrated sunlight to power,including electrical power. In some embodiments, the solar receivers cancomprise back-contact, back junction solar cells, while in others,front-contact or other cells can be used. In certain embodiments, thesolar receivers 132, 134, 152, 154 can be supported independently fromthe concentrator elements, such as by a support assembly coupled to thecrossbeam 104.

Each solar receiver 132, 134, 152, 154 is preferably coupled to aconcentrator element in a position such that reflected, concentratedsunlight impinges it at a predetermined angle. It is desirable that theincoming concentrated sunlight impinges at a 90° angle to the surface ofthe solar receiver 132, 134, 152, 154. Thus, each solar receiver ispreferably mounted in such a position that the surface of each solarreceiver 132, 134, 152, 154 is at a right angle, or as nearly a rightangle as practicable, to the anticipated angle of impinging concentratedsunlight from each concentrator element 122, 124, 126, 142, 144, 146, aswill be explained in greater detail below.

Because the solar concentrator assembly 100 operates most efficientlywhen the maximum available sunlight is received by the concentratorelements 122, 124, 126, 142, 144, 146, the torque tube 106 can berotated during daily operation to adjust the position of the crossbeam104 and other cross-pieces. This in turn changes the orientation of theconcentrator elements 122, 124, 126, 142, 144, 146, which can bepositioned to advantageously and desirably receive as much sunlight aspossible.

FIGS. 3 and 4 illustrate another embodiment of a solar concentratorassembly 200. Unless otherwise noted, the numerical indicators refer tosimilar elements as in FIGS. 1 and 2, except that the number has beenincremented by 100.

FIG. 3 illustrates a solar concentrator assembly 200 in a first, rotatedposition. As can be seen, the torque tube 206 has been rotatedclockwise, which would correspond to tracking the sun to a position tothe right of the post 202. Preferably, the torque tube 206 is rotated bya drive mechanism which is, in turn, operated by a control system. Thecontrol system can include a processor, sensors, and other components totrack the sun and adjust the orientation of the solar concentratorassembly 200 as desired.

Thus, the orientation shown in FIG. 3 is the result of rotating thesolar concentrator assembly 200 to follow the course of the sun throughthe sky. As can be seen, the solar concentrator assembly 200 rotatesaround the axis of rotation 290 of the torque tube 206. It is desirablethat the center of gravity of the portion of the solar concentratorassembly 200 supported by the torque tube 206 coincide as closely aspossible with the axis of rotation 290. This is accomplished byarrangement of the groups of concentrator elements 220, 240 into theassembly shown.

Specifically, the torque tube 206 is positioned between the first andsecond groups of concentrator elements 220, 240. Each concentratorelement in the first group of concentrator elements 220 faces in adifferent direction than each concentrator element in the second groupof concentrator elements 240. Thus, the two concentrator elements 222,242 nearest the torque tube 206 have their rear sides both facing thetorque tube 206. Each concentrator element 222, 242 also has areflective front side facing away from the torque tube 206. Eachconcentrator elements in the same group of concentrator elements 220,240 have the same orientation.

This arrangement of concentrator elements permits the torque tube 206 tobe positioned above the crossbeam 204, unlike other concentratorassemblies where the crossbeam 204 is above the torque tube 206. In suchassemblies, the center of gravity is offset from the center of rotationof the torque tube 206. Such an offset results in a moment about thecenter of rotation as the center of gravity is acted on by gravity. Thismoment introduces torque tube twist, which introduces misalignment andundesirable deformation to the assembly. By positioning the first andsecond groups of concentrator elements 220, 240 as shown, the torquetube 206 can be positioned to rotate about its axis 290 which iscoincident with the center of gravity of the entire assembly.

In some embodiments, the axis of rotation 290 is coincident with thecenter of gravity of the assembly, while in others, the center ofgravity is positioned within the torque tube, although it may beslightly offset from the axis of rotation 290. Preferably, however, anysuch offset is minimized.

FIG. 4 illustrates the solar concentrator assembly 200 experiencing windconditions illustrated by profile U. The force of wind experienced atconcentrator element 246 is shown as F₁. The force of wind experiencedat concentrator element 244 is shown as F₂. Typically, the wind profileU has a higher velocity with increasing altitude from the ground. Thus,the wind force experienced at concentrator element 226 is higher thanthe wind force experienced at concentrator element 246. Thus, F₂ istypically higher than F₁. This relationship continues through F₃.

Each force F₁, F₂, F₃ is exerted against a respective concentratorelement 246, 244, 242. Because each concentrator element 246, 244, 242is offset from the axis of rotation 290, a resultant moment M₁ iscreated about the axis of rotation 290. In the relationship illustrated,the moment M₁ is clockwise about the axis of rotation 290. The magnitudeof the moment M₁ is determined in part by the velocity of the windprofile U, but also by the apparent cross-section of the concentratorelements 246, 244, 242 against which the wind forces F₁, F₂, F₃ areexerted. As can be seen, the clockwise rotation of the solarconcentrator assembly 200 positions the second group of concentratorelements 240 to present a larger cross-section to the wind profile U.

In addition to the benefit of permitting the torque tube 206 to bepositioned above the crossbeam 204 and, therefore, the axis of rotation290 coincident with the center of gravity, by arranging the concentratorelements as shown, the profile of the first group of concentratorelements 220 is turned into the wind profile U such that only across-section of the concentrator elements 222, 224, 226 is exposed tothe wind profile U. The counterforce CF₁ exerted by the wind profile Uagainst the concentrator element 226 contributes to a counter-moment CM₁which is in the opposite direction to the moment M₁. Accordingly, themoment M₁ is resisted in part by the forces CF₁, CF₂, and CF₃experienced by concentrator elements 226, 224, 222, respectively.

Most desirably, the counter-moment CM₁ would be equal in magnitude tothe moment M₁, but in the opposite direction, resulting in only dragwind loads being imparted to the torque tube 206. The arrangement andorientation of concentrator elements as shown contributes to equalizingthe magnitudes of M₁ and CM₁. This is because the higher-elevated firstgroup of concentrator elements 220 experiences higher wind forces CF₁,CF₂, CF₃ because they are higher in the wind profile U. Thecross-section presented by the first group of concentrator elements 220is, however, smaller than that presented by the second group ofconcentrator elements 220. The balance between the higher force andsmaller cross-section of the first group of concentrator elements 220and the lower force, but larger cross-section of the second group ofconcentrator elements 240 minimizes, reduces, and inhibits unequalmoments M₁ and CM₁, thereby reducing the moment experienced by thetorque tube 206. This is another advantage of the arrangementillustrated in FIGS. 1-4, in addition to the inhibition of torque tubetwist.

FIG. 5 illustrates a detailed view of a portion of a solar concentratorassembly 300. Unless otherwise noted, the numerical indicators refer tosimilar elements as in FIGS. 1 and 2, except that the number has beenincremented by 200.

The sun 360 radiates sunlight 362. The concentrated sunlight 362 isreflected by concentrator element 322 as concentrated sunlight 364toward the first solar receiver 332. A top edge of concentrated sunlight366 travels from the top edge of the concentrator element 322 a certaindistance to reach the first solar receiver 332. A bottom edge ofconcentrated sunlight 368 travels a different distance from the bottomedge of the concentrator element 322 to reach the first solar receiver332. It is desirable that the top edge of concentrated sunlight 366travel downward as little as possible while covering the distance to thefirst solar receiver 332. Similarly, it is desirable that the bottomedge of concentrated sunlight 368 travel to the first solar receiver 332as vertically as possible, reducing forward travel toward the adjacentconcentrator element 324. The result of these desirable improvements isthat the band of focused sunlight impinging on a solar receiver has aneven profile, with reduced or eliminated variation in intensity.

It should be understood that although the top and bottom edges ofconcentrated sunlight 366, 368 are illustrated impinging onsubstantially entirely the face of the first solar receiver 332, inpractice, the band of concentrated sunlight can be narrower and focusedon a solar cell positioned at a desired location on the face. Thus, anarrow band of concentrated sunlight can be reflected to the middle ofthe first solar receiver 332 and, preferably, to the middle of the solarcell. If the concentrated sunlight band impinges only on a middleportion of the solar cell, small misalignment errors will have a reducedeffect on efficiency as the concentrated sunlight will still impinge thesolar cell, even if slightly off target.

The inventors have discovered that offsetting at least some of theconcentrator elements 322, 324, 326 in a vertical direction as theyproceed outward from the torque tube 306 permits advantageousgeometrical characteristics to the reflector/receiver arrangement overconcentrator elements positioned at the same height relative to oneanother. Thus, the first concentrator element 322 is positioned at aheight of h₁. The second concentrator element 324 is offset verticallyto a height of h₂, which is greater than h₁. The third concentratorelement 326 is offset vertically to a height of h₃, which is, in turn,greater than h₂. These heights are measure relative to the referenceheight of the bottom of the reflector component of concentrator element322.

Angle α is indicative of the angle of constant vertical offset of theconcentrator elements from a horizontal axis, as shown. Accordingly,angle α has a value greater than 0°, preferably approximately 5°. Thus,the exact value of the height difference can vary between embodiments solong as a consistent offset is used. In some embodiments, a non-linearoffset can be used, such that the value of difference between h₁ and h₂can be greater than the value of the difference between h₁ and h₀. Forconcentrators spaced equally in the horizontal direction, a non-lineararrangement results.

The solar receivers 332, 334 can be have a different orientation whencoupled to concentrator elements 322, 324, 326 offset in a verticaldirection than when coupled to concentrator elements without thevertical offset. The different orientation can be solely a rotationabout an axis extending through a portion of the receiver, or can be orinclude a translation in the horizontal or vertical directions, in someembodiments. Preferably, however, a solar receiver does not protrudebeyond the overhanging upper portion of the concentrator element towhich it is coupled, and therefore does not cast a shadow on a portionof the concentrator element below.

Additionally, the cross-sectional shape of the concentrator elements322, 324, 326 can be altered from a shape used for concentrator elementswithout a vertical offset. Although both shapes can have a paraboliccharacteristic, those concentrator elements 322, 324, 326 verticallyoffset can have a slope which reflects light collectively more upwardlythan a reflective surface of concentrator elements without verticaloffset.

The height difference between the concentrator elements need not displaya similar height difference from a horizontal crossbeam 304. As shown,the crossbeam 304 can have an upward cant substantially the same asangle α, or, in some embodiments, it can be horizontal. Similarly,cross-pieces of the solar concentrator assembly 300 can have a similarshape as the crossbeam 304, or a different one.

FIG. 6 illustrates a detailed view of a portion of a solar concentratorassembly 400. Unless otherwise noted, the numerical indicators refer tosimilar elements as in FIGS. 1 and 2, except that the number has beenincremented by 300.

FIG. 6 illustrates an embodiment in which the two concentrator elementsdepicted 422, 424 are at the same height h₀, or without vertical offset.Three additional reference lines are added to illustrate principlesdiscovered by the inventors to advantageously increase efficiency of thesolar concentrator assembly. First, a lower edge normal 469 is shownextending upwardly in a direction normal to, and from, the lower edge ofthe reflective side of the first concentrator element 422. The loweredge of the reflective side of the first concentrator element 422 ispreferably in a vertically-extending plane with the upper edge of thesecond concentrator element 424. In this way, no sunlight is lostbetween the concentrator elements 422, 424. The bottom edge ofconcentrated sunlight 468 forms an angle θ₀ with the lower edge normal469.

The first solar receiver 432 is shown mounted to the rear side of thesecond concentrator element 424. A mounting component in addition to asolar panel or cell portion can comprise the solar receiver 432, asexplained above. The solar receiver 432 receives the bottom edge ofconcentrated sunlight 468 at an angle, which depends on both the tilt ofthe solar receiver 432 and the parabolic shape of the reflective side ofthe concentrator element 422. Preferably, the angle θ₀ is minimized toavoid inefficient sunlight transfer between the concentrator element 422and the solar receiver 432. Such inefficiency can occur whenconcentrated sunlight 464 travels through a glass surface of the solarreceiver 432. Even with anti-reflective coating, some scattering isunavoidable, and should be minimized to reduce the inefficiency of lighttravel through the surface of the solar receiver 432.

The solar receiver 432 has a normal direction 433 which is located at aright angle to the plane of the receiving surface of the solar receiver432. The normal direction 433 is preferably directed at the center ofsunlight received from the concentrator element 422. The center ofsunlight is not necessarily the geometric center of the parabolic shapeof the reflective surface of the concentrator element 422, but insteadis a weighted average of sunlight from the entire reflective surface ofthe concentrator element 422. As concentrated sunlight 464 is moredirectly received from the lower portion of the reflective surface, thevalue of sunlight from this region is increased relative to, forexample, concentrated sunlight 464 received at the solar receiver 432from near the top edge of concentrated sunlight 466. Accordingly, thenormal direction 433 typically is positioned more towards the bottomedge 468 than the top edge 466 of concentrated sunlight.

Additionally, light that impinges on the surface of the solar receiver432 at a smaller angle to the normal direction 433 is more efficientthan light which arrives at a larger angle to the normal direction 433.Thus, light which has a smaller incident angle to the surface of thesolar receiver 432 is more desirable. In some embodiments, ananti-reflective coating can be applied to the surface of the solarreceiver 432. One advantage to decreasing the incident angle ofconcentrated sunlight 464 arriving at the surface of the solar receiver432 is that anti-reflective coating can be omitted without reducingefficiency, resulting in a cost savings.

Finally, an upper edge normal 467 extends perpendicularly to thereflective surface at the top edge of the concentrator element 422 asshown. The top edge of concentrated sunlight 466 forms an angle β₀ withthe upper edge normal 467. It is desirable to reduce the angle β₀ forreasons similar to the advantage to reducing angle θ₀. Moreover,unconcentrated sunlight 462 is reflected by the reflective surface ofconcentrator element 422 increasingly, that is, with less scatteredlight, as angle θ₀ decreases.

FIG. 7 illustrates a detailed view of a portion of a solar concentratorassembly 500. Unless otherwise noted, the numerical indicators refer tosimilar elements as in FIG. 6, except that the number has beenincremented by 100.

In FIG. 7, the second concentrator element 524, to which the solarreceiver 532 is mounted, has been vertically offset to a height h₁. Thisvertical offset has an advantageous effect on each of the threecharacteristics described above with respect to FIG. 6. FIGS. 6 and 7are not to scale and distances or angles may be exaggerated to valueseither larger than actual measures or proportions or smaller fordescriptive purposes.

First, the angle θ₁ has been reduced. For reasons presented above, thisincreases efficiency of the solar receiver 532 by adjusting the angleconcentrated sunlight 564 at or near the bottom edge of concentratedsunlight 568 travels through the surface of the solar receiver 532.Additionally, the reflectance of the mirrored surface of the solarconcentrator 522 is increased because the incident angle ofunconcentrated sunlight 562 is decreased.

Second, to continue to direct the normal direction 533 at the weightedaverage center of concentrated sunlight 564 from the reflective surfaceof the concentrator element 522, the angle of the surface of the solarreceiver facing concentrator element 522, and receiving concentratedsunlight 564 therefrom, has been changed downward. Accordingly, thenormal direction 533 has also been directed downward relative to theposition in FIG. 6. Additionally, the shape of the reflective surface ofthe concentrator element 522 has been adjusted to a different parabolicshape which directs concentrated sunlight 564 in a greater concentrationtowards the bottom edge 568 than that of FIG. 6. This is advantageousfor reasons similar to the benefit that results from a smaller angle θ₁.

Third, angle θ₁ is likewise reduced. This additionally increases theefficiency of the solar concentrator assembly. Similarly to howdecreasing angle θ₁ improves the reflectivity of the surface of theconcentrator element 522 for sunlight reflected near the lower edge, thedecreasing angle β₁ increases the reflectivity of the mirror near theupper edge. This increase in reflectivity results in more concentratedsunlight 564 reflected toward the solar receiver 532 from near the upperedge. Moreover, these effects extend across the face of the entirereflective surface of the concentrator element 522, improvingreflectance of the unit as a whole.

In addition to these three exemplary advantages which result from thevertical offset of the concentrator elements, the solar receiver 532 canbe enlarged, as shown in FIGS. 6 and 7, while maintaining the sameapproximate position relative to the surface of the solar concentrator522. This is increased size of the solar receiver 532 can enable sizingchanges or additional components to be added to the solar receiver 532.For example, a larger heat sink can be incorporated into the solarreceiver 532. A larger heat sink can reduce the operating temperature ofthe solar cell included in the solar receiver 532. By decreasing theoperating temperature, the efficiency of the solar cell can beincreased, resulting in an overall performance improvement to thesystem.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

What is claimed is:
 1. A solar concentrator assembly comprising: a firstreflective device having a first reflective front side and a first rearside; a second reflective device having a second reflective front sideand a second rear side, wherein the first and second reflective frontsides face away from one another; a third reflective device having athird reflective front side and a third rear side; and a supportassembly coupled to and supporting the first, second, and thirdreflective devices, the third reflective device positioned to bevertically offset from the first and second reflective devices.
 2. Thesolar concentrator assembly of claim 1, wherein the support assemblycomprises a crossbeam supporting the first, second, and third reflectivedevices, wherein the third reflective device is positioned farther fromthe crossbeam than the first and second reflective devices.
 3. The solarconcentrator assembly of claim 1, wherein the third reflective device ispositioned such that the second reflective front side of the secondreflective device faces the third rear side of the third reflectivedevice.
 4. The solar concentrator assembly of claim 3, wherein thesecond reflective device is vertically offset from the first reflectivedevice.
 5. The solar concentrator assembly of claim 3, furthercomprising a first solar receiver coupled to the third rear side of thethird reflective device and positioned to receive light reflected fromthe second reflective front side.
 6. The solar concentrator assembly ofclaim 1, further comprising a torque tube positioned between the firstrear side of the first reflective device and the second rear side of thesecond reflective device.
 7. The solar concentrator assembly of claim 6,further comprising a fourth reflective device having a fourth reflectivefront side and a fourth rear side, the fourth reflective devicevertically offset from the first reflective device.
 8. The solarconcentrator assembly of claim 7, wherein the fourth reflective deviceis positioned such that the first reflective front side of the firstreflective device faces the fourth rear side of the fourth reflectivedevice.
 9. The solar concentrator assembly of claim 8, furthercomprising a second receiver coupled to the fourth rear side of thefourth reflective device and positioned to receive light reflected fromthe first reflective front side.
 10. The solar concentrator assembly ofclaim 1, wherein the first reflective front side has a parabolic shape.11. A solar concentrator assembly comprising: a torque tube having along axis; a crossbeam extending in a direction transverse to the longaxis; a first reflective device having a first reflective front side anda first rear side, the first reflective device supported by thecrossbeam at a first height; a second reflective device having a secondreflective front side and a second rear side, the second reflectivedevice supported by the crossbeam at a second height, wherein the firstand second reflective front sides face away from one another, andwherein the torque tube is positioned between the first rear side andthe second rear side; and a third reflective device having a thirdreflective front side and a third rear side, the third reflective devicesupported by the crossbeam at a third height greater than the first andsecond heights.
 12. The solar concentrator assembly of claim 11, whereinthe third reflective device is positioned such that the secondreflective front side of the second reflective device faces the thirdrear side of the third reflective device.
 13. The solar concentratorassembly of claim 12, further comprising a first solar receiver coupledto the third rear side of the third reflective device and positioned toreceive light reflected from the second reflective front side of thesecond reflective device.
 14. The solar concentrator assembly of claim13, further comprising a fourth reflective device having a fourthreflective front side and a fourth rear side, the fourth reflectivedevice supported by the crossbeam at a fourth height and positioned suchthat the first reflective front side of the first reflective devicefaces the fourth rear side of the fourth reflective device.
 15. Thesolar concentrator assembly of claim 14, wherein the first height andthe second height are substantially the same, and wherein the thirdheight and the fourth height are substantially the same.
 16. The solarconcentrator assembly of claim 14, further comprising a second solarreceiver coupled to the fourth rear side of the fourth reflective deviceand positioned to receive light reflected from the first reflectivefront side of the first reflective device.
 17. A solar array comprising:a crossbeam extending along a first axis; a torque tube intersecting thecrossbeam near the center of the crossbeam, the torque tube extendingalong a second axis, the second axis substantially transverse to thefirst axis; a first solar concentrating device having a first reflectivesurface and a first back surface opposite the first reflective surface,the first solar concentrating device coupled to the crossbeam at a firstheight; a second solar concentrating device having a second reflectivesurface and a second back surface opposite the second reflectivesurface, the second solar concentrating device coupled to the crossbeamat a second height, the first and second reflective surfaces facing awayfrom one another; and a third solar concentrating device having a thirdreflective surface and a third back surface opposite the thirdreflective surface, the third solar concentrating device coupled to thecrossbeam at a third height, wherein the third solar concentratingdevice is positioned farther along the crossbeam from the torque tubethan the first and second solar concentrating devices, and wherein thethird height is higher than the first and second heights.
 18. The solararray of claim 17, wherein the torque tube is positioned between thefirst back surface and the second back surface.
 19. The solar array ofclaim 18, wherein the second solar concentrating device and the thirdsolar concentrating device are positioned such that the secondreflective surface faces the third back surface.
 20. The solar array ofclaim 19, further comprising a solar receiver coupled to the third backsurface of the third solar concentrating device and positioned toreceive light reflected from the second reflective surface of the secondsolar concentrating device.